Search results for "Geophysics"
showing 10 items of 2645 documents
Characteristic time scale of auroral electrojet data
1994
The structure function of the AE time series shows that the AE time series is self-affine such that the scaling exponent changes at the time scale of approximately 113 (±9) minutes. Autocorrelation function is shown to have scaling properties similar to those of the structure function. From this result it can be deduced that the time scale at which the scaling properties of the AE data change should equal the typical autocorrelation time of these data. We find the typical autocorrelation time of the AE data is 118 (±9) minutes. The characteristic time scale of the AE data appears as a spectral break in their power spectrum at a period of about twice the autocorrelation time.
EARLY NEOPROTEROZOIC CRUST FORMATON IN THE DZABKHAN MICROCONTINENT, CENTRAL ASIAN OROGENIC BELT
2017
The Dzabkhan microcontinent was defined by [Mossakovsky et al., 1994] as a cratonic terrane with an early Precambrian basement that combines highgrade metamorphic complexes of the Songino, Dzabkhan, Otgon, Baidarik, Ider and Jargalant Blocks. However, early Precambrian ages have so far only been recognized in the Baidarik and Ider blocks [Kozakov et al., 2007, 2011; Kroner et al., 2015].
The Mycenaean drainage works of north Kopais, Greece: a new project incorporating surface surveys, geophysical research and excavation
2013
The attempt to drain the Kopais Lake was one of the most impressive and ambitious technical works of prehistoric times in Greece, inspiring myths and traditions referring to its construction and operation. The impressive remnants of the Mycenaean hydraulic works represent the most important land reclamation effort during prehistoric Greek antiquity, thus attracting the attention of the international scientific community. Nevertheless, in spite of the minor or extended contemporary surveys, the picture of the prehistoric drainage works in Kopais has remained ambiguous. Concerning the function of these works and their precise date within the Bronze Age, the proposed theories were based solely…
Magnetic imaging of a late Bronze Age tumulus in France before and during excavation
2002
Geophysical surveying is taking place in the Chatillon-sur-Seine area in France to examine and map prehistoric settlements and the structure of tumuli (grave-mounds which originally reached a height of up to 5 m but which are now almost level). The magnetic survey discussed here was conducted to detect archaeological structures within a late La Tene (100-50 bce) necropolis, in particular the preexcavation recording of a late Bronze Age round barrow. During the excavation, additional surveys were carried out to analyze the influence of immediate subsurface soil layers on the magnetic anomalies originating from the deeper archaeological features. Additional radar surveys made use of a 500 MHz…
Evaluation of positron-emission-tomography for visualisation of migration processes in geomaterials
2008
Abstract Positron-emission-tomography (PET) was applied for direct visualisation of solute transport in order to overcome the limitations of conventional methods for measuring advection and diffusion properties. At intervals from minutes to days the 3D-spatial distribution of the PET-tracer is determined. This spatiotemporal evolution of the tracer concentration can be used as experimental basis for clarification of the relevant transport processes, derivation of transport parameters, and model calibration. Here, 18 F and 124 I in 0.01 M carrier solution of KF and KI, respectively, have been chosen out of the limited number of available PET-tracers, primarily on account of their decay time …
Propagation of errors due to incorrect positions of sources and detectors in wave-field tomography
2004
Tomographic data processed by 2D inversion programs can produce fairly large distortions due to incorrect source and/or detector positions. This problem is very serious in high-frequency electromagnetic tomography (GPR), due to the dimensions of the transmitter and receiver antennae. The errors can even be larger when coupled antennae are used (receiver and transmitter inside the same box) whose positions are not clearly known. Similar errors can be involved in seismic tomography, for instance when the mechanical connection between transducers and sample is defective. In this paper the problem has been studied using synthetic data which were calculated for different acquisition geometries. …
Geochronology and palaeomagnetism of a late Proterozoic island arc terrane from the Red Sea Hills, northeast Sudan
1992
Abstract Size fractions and single grains of zircon, hornblende and biotite have been dated to define the formation age and thermal history of the northern Haya Terrane (NHT), a late Proterozoic island arc terrane of the Red Sea Hills (RSH), northeast Sudan. U Pb and 207 Pb/ 206 Pb zircon data for acidic volcanics and granitoid rocks bracket the time of formation of the NHT between 887 ± 20 and 854 ± 9 Ma. 40 Ar/ 39 Ar hornblende and biotite ages of a gabbro near Suakin suggest passage through the argon closing temperature for hornblende at about 841 ± 4 Ma and 782 ± 6 Ma for biotite. The hornblende age is considered to be representative of the age of magnetic blocking and, hence, the age o…
Modeling of retrograde diffusion zoning in garnet: evidence for slow cooling of granulites from the Highland Complex of Sri Lanka
2003
¶Diffusion modeling of zoning profiles in garnet rims from mafic granulites is used to estimate cooling rates in the Proterozoic basement of Sri Lanka, which represents a small, but important fragment of the Gondwana super-continent. Metamorphic peak temperatures and pressures, estimated with two-pyroxene thermometry and garnet–clinopyroxene–plagioclase–quartz (GADS) barometry, yield 875±20 °C and 9.0±0.1 kbar. These peak metamorphic conditions are slightly higher than results obtained by garnet-biotite Fe–Mg exchange thermometry of 820±20 °C. Reset flat zoning profiles were observed in most garnets. Only narrow garnet rims touching biotite exhibit retrograde zoning in terms of Fe and Mg ex…
Mineralogical and Chemical Records of Icelandic Dust Sources Upon Ny-Ålesund (Svalbard Islands)
2018
This work aims to identify the geochemical and mineralogical markers of Icelandic dust and to differentiate it from the dust of local origin deposited at the Ny-Ålesund station. We characterized representative sediment samples from Iceland and Svalbard and compared them to a set of aerosol samples collected in Ny-Ålesund to check the existence and type of the mineralogical markers. The sediment samples were analyzed by X-ray diffraction (XRD) to detect the mineralogical constrain of the geochemical markers. Both aerosol and sediment samples were examined by scanning electron microscopy coupled with EDS microanalysis (SEM-EDS) and image analysis to detect and to provide a morpho-chemical cha…
Rutile crystals as potential trace element and isotope mineral standards for microanalysis
2009
Abstract The present paper reports trace element concentrations of 15 elements (V, Cr, Fe, Zr, Nb, Mo, Sn, Sb, Hf, Ta, W, Lu, Pb, Th and U) as well as Pb and Hf isotope data for four relatively homogeneous and large (centimeter size) rutile grains. Methods employed are SIMS, EMP, LA-ICP-MS, ID-MC-ICP-MS and TIMS. For most elements homogeneity is usually within ± 10% and occasionally variations are even narrower (± 5%), particularly in the core of two of the studied grains. The trace element concentrations of the grains span a broad compositional range (e.g., Zr concentrations are ca. 4, 100, 300 and 800 ppm). Provisional concentration values, calculated based on the homogeneity of the eleme…